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290           MOEPHOLOGY AND EVOLUTION
bifurcation appears on the outer aspect of the hemisphere.
The collateral sulcus is long. It has several branches, and it bifurcates posteriorly. Several little sulci are arranged alongside it.
The calloso-marginal sulcus is well marked.
A mesial section through the corpus callosum and lower parts of the brain reveals how the general appearances are much as in Man, and a series of horizontal sections reveals how the basal ganglia have also an identical disposition. The hind brain shows a reduced paraflocculus in some cases, and equal flocculi and paraflocculi in others.
THE BRAIN IN THE GORILLA (fig. 51).
Of all the Apes the Gorilla has the largest brain, and the cerebral characters resemble those of Man most closely. The frontal lobes are rostrated.
The central sulcus (C.S.) has a genu. It may not pass on to the mesial aspect of the hemisphere, and it may be connected to the Sylvian fissure by a groove. The superior frontal (S.F.S.) and superior precen-tral sulci form a triradius, and a middle frontal sulcus (M.F.S.) lies anteriorly between the superior frontal sulcus and sulcus rectus (S.B.). The latter varies in different brains, but it forms a triradius with the arcuate or inferior precentral sulcus (I.P.S.). The arcuate sulcus sometimes passes into the central sulcus. In fig. 51 it is seen to pass into the Sylvian fissure; so it may represent the arcuate and inferior transverse sulci *of the Orang. There may be a fronto-marginal sulcus of Wernicke.